OBJECTIVES The student will be able to Draw

OBJECTIVES The student will be able to… • Draw a plant with a “phototropic response” to light. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

OBJECTIVES The student will be able to… • Detail what would need to be done to cause a poinsettia to flower. • State how light intensity affects foliage color and give two examples. • Describe how latitude, time of year, elevation, time of day, and region affect light intensity. • Name several units of light measurement and specify which is most common in horticulture. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

OBJECTIVES The student will be able to… • Given a room in which plants will be grown, give a listing of ten indoor species and where they could be positioned relative to the windows to receive the correct amount of light. • Given a similar room, suggest three ways that the natural light in the room could be maximized. • Draw the spectrum of visible light and indicate the principal wavelengths of importance in plant growth. • List two symptoms of excess light in plants and two symptoms of insufficient light. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

EFFECT OF LIGHT ON GROWTH/DEVELOPMENT • Light is essential for photosynthesis, and without it, chlorophyll, carbohydrates, hormones, and many other plant-manufactured chemicals can’t be made. – Plants grown in insufficient light do not stop growing • They develop abnormally long stems with relatively few leaves, which leads to a stringy or lanky look. – During etiolation, the plant respires stored carbohydrates. • When most of the carbohydrate has been respired, it will die. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

EFFECT OF LIGHT ON GROWTH/DEVELOPMENT Figure 17 -1 Etiolation of a plant due to insufficient light. Both plants have the same number of leaves and were propagated at the same time, but the plant on the right received less light. Kirk Zirion photo. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

EFFECT OF LIGHT ON GROWTH/DEVELOPMENT Phototropism and Similar Responses • Phototropism is the growth of a plant toward light. – Auxin is pumped to the side of the stem away from the light, which then lengthens. • Because the sides of the stem grow at different rates, the stem curves in the direction of light. The “seeking” of light by plants is actually a hormonal response. In other plants, differences in light level change the leaf form. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. Figure 17 -2 Phototropism caused by light reaching the plant from only the left side. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

EFFECT OF LIGHT ON GROWTH/DEVELOPMENT Phototropism and Similar Responses Cutleaf philodendron (Monstera deliciosa) shows a different reaction to varying light levels The number of splits contained by new leaves decreases at lower light levels. A plant growing in poor light may have no splits at all, whereas one growing in moderate light may have several in each leaf. Figure 17 -3 Splitting philodendron (Monstera deliciosa) leaves is a function of light intensity. The unsplit leaf developed in dim light, the split leaves in brighter light. Rick Smith photo tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

EFFECT OF LIGHT ON GROWTH/DEVELOPMENT Light and Flowering - Photoperiod • Insufficient light intensity can inhibit the flowering of many plants grown indoors. – Relatively bright light intensities are necessary to trigger flowering in most cultivated plants. • Not often available indoors. • Plants can be classified with regard to photoperiod – As short day, long day, or day neutral. • Photoperiod refers to day/night ratio of each 24 -hour period, affects flowering, tuber & bulb formation. – Correct photoperiod combined with sufficient light intensity causes or hastens flowering in some indoor plants. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

EFFECT OF LIGHT ON GROWTH/DEVELOPMENT Light and Flowering - Photoperiod • A few indoor plants, such as chrysanthemum and poinsettia require specific photoperiods to bloom. See the entire table on page 322 of your textbook. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

EFFECT OF LIGHT ON GROWTH/DEVELOPMENT Light and Flowering - Photoperiod • Many indoor plants are tropical, from regions near the equator where day length varies little all year. – Most are day neutral and flower because of combinations of age, light intensity, and temperature. • Time a photoperiodic plant must be kept under correct day/night lengths to trigger flowering varies. – If not maintained long enough, the plant may revert to its vegetative state, ceasing bud development. . – A short-day plant on a long-night schedule too long will lose valuable photosynthetic time and may lose vigor. – Schedule should be maintained until the flower buds are completely developed. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

EFFECT OF LIGHT ON GROWTH/DEVELOPMENT Light and Flowering - Photoperiod • Most houseplants in which photoperiod controls flowering are short-day plants, needing daily periods of uninterrupted darkness before flowering occurs. – Darkness should be checked by standing inside with the door closed—cover leaks or use another closet. – Poinsettias are very sensitive, and bloom will be delayed if the dark period ever is broken by light, or is not absolute. • Flowering long-day plants are simply left in a room used in the evenings. – Artificial lights supplement the natural day length with enough light to total 14 or more hours, and blooms will be initiated. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

EFFECT OF LIGHT ON GROWTH/DEVELOPMENT Light and Plant Health - Foliage • Foliage Color - in many instances the darker the foliage of a plant, the less light it requires. – Common plants that grow well in dim light—snake plant, rubber plant, cast iron plant, Chinese evergreen, and philodendron—all have deep green foliage. • When grown with little light, they develop a dense chlorophyll layer near leaf surfaces, making them efficient users of light. • Many, such as variegated spider plant, tricolor dracaena, and variegated wandering Jew, require more light than their nonvariegated relatives. – Lacking chlorophyll in the white areas of the leaves, they require more or brighter light to compensate. • Many plants with red coloring pigments also need bright light. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

EFFECT OF LIGHT ON GROWTH/DEVELOPMENT Light and Plant Health • Fleshy/Succulent Plants with thickened leaves and/or stems such as jade, kalanchoe, and cacti require more light than do those with thin leaves. – Fleshy structure minimizes surface area vulnerable to transpiration water loss, helping survive in dry climates. • Photosynthesizing area is reduced, so these plants can be grown indoors more successfully in bright-light locations. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

EFFECT OF LIGHT ON GROWTH/DEVELOPMENT Light and Plant Health - Native Conditions • A plant that grows naturally in the shade of other plants is usually better adapted to indoor growing than a plant accustomed to unobstructed sunlight. – Ferns grow naturally in the shade of trees, and also grow well in a dim area indoors, a generalization for many tropical plants. • Devil’s ivy, peperomia, and arrowhead. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

EFFECT OF LIGHT ON GROWTH/DEVELOPMENT Light Intensity • Natural light intensity is affected by geographical or altitudinal variation, and climatic factors. – Light intensity and duration are factors contributing to the total light a plant receives. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

EFFECT OF LIGHT ON GROWTH/DEVELOPMENT Light Intensity - Latitude • Latitude - due to the way the Earth is oriented in space, the sun rises exactly in the east, and sets exactly in the west only at the equator. In the Northern Hemisphere, the sun will always appear slightly in the southern sky. Figure 17 -4 a Typical positions of the sun in (a) winter and (b) summer in the Northern Hemisphere. Note the sun remains in the South and that the positions of rising and setting differ with the season. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

EFFECT OF LIGHT ON GROWTH/DEVELOPMENT Light Intensity - Latitude • By hitting Earth’s atmosphere at an angle instead of directly above, the distance light must travel through the atmosphere to reach the Earth is increased. – Light is lost in the atmosphere & the further north one lives, the less the light intensity. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

EFFECT OF LIGHT ON GROWTH/DEVELOPMENT Light Intensity - Time of Year • The sun stays in the southern sky over the year, and drops lowest toward the southern horizon in winter. – Approaching closest to directly overhead at midday in summer, with the change in angle dependent on the distance from the equator. Figure 17 -4 a Typical positions of the sun in (a) winter and (b) summer in the Northern Hemisphere. Note the sun remains in the South and that the positions of rising and setting differ with the season. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

EFFECT OF LIGHT ON GROWTH/DEVELOPMENT Light Intensity - Time of Day • Midday, the sun at its highest point, provides the greatest intensity of light. – In either morning or evening the sun is lower toward the horizon & intensity decreases due to the distance it is penetrating through the atmosphere. • Local daily weather variation can change intensity. – Out West, foggy mornings lessen early-day light intensity. • The afternoon sun is much brighter in these areas. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

EFFECT OF LIGHT ON GROWTH/DEVELOPMENT Light Intensity - Altitude • People living at high altitudes (over 1, 000 feet above sea level) frequently receive greater light intensity than would be expected at their latitude. – Air is less dense, the atmospheric layer is thinner at high altitudes, and less light intensity is lost passing through it. • Denver, Colorado, at over 5, 000 feet in altitude, has substantially higher light intensity, year-round than Boston, Massachusetts – Even though the two are less than 4 deg latitude apart. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

EFFECT OF LIGHT ON GROWTH/DEVELOPMENT Light Intensity - Clouds, Fog, and Smog • In cloud-, fog-, or smog-covered areas, light intensity is habitually lower than clear areas. – Water vapor or pollution haze acts as a reflector, sending much of the sunlight back toward space. • They also diffuse sun rays, giving the Earth shadowless illumination, not a sun/shadow pattern of direct sunlight. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

EFFECT OF LIGHT ON GROWTH/DEVELOPMENT Light Intensity - Snow/Sand • Persistent snow cover affects light intensity by reflecting sunlight indoors. – Cold areas with snow cover most of the winter receive a slightly increased amount of light through all windows because of this reflection. • This principle applies to houses surrounded by lightcolored sand, white rock mulch, or similar material. – Although dark soil will absorb light, light sand reflects it and will increase the light entering a house. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

EFFECT OF LIGHT ON GROWTH/DEVELOPMENT Light Duration • Light duration (day length) is another component of total light. – Increased duration can help compensate for low intensity, but below a certain minimum, will not help. • Equatorial days & nights are equal in length all year. – In the North, 9 hour winter days & 15 hour summer days are not uncommon, as a result of latitude. • More pronounced the further north one travels. • The shortest winter days correspond with the period when the sun is lowest on the horizon —reaching a climax around December 22, the winter solstice. – At this point the sun again begins moving toward the northern sky and days begin to lengthen. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

EFFECT OF LIGHT ON GROWTH/DEVELOPMENT Light Duration Coding the continental U. S. into bright-, medium-, and dim-light areas for winter and summer. Bear in mind that for most areas, summer light is three to four times as great as winter light. Figure 17 -5 b Mean daily solar radiation throughout the U. S. in January and July. University of Texas Libraries. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

EFFECT OF LIGHT ON GROWTH/DEVELOPMENT • Measuring light in relation to plant growth is a complex topic that can be broken into three subtopics: tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

EFFECT OF LIGHT ON GROWTH/DEVELOPMENT Finding Total Solar Radiation Entering Windows • Total light entering windows is of great importance. – Measure with a thermopile or bolometer with a flat response—not favoring reading any partiular wavelength. • It is an incident light meter because it measures light intensity falling on an object, in this case a plant. – A representative reading takes measurements at several parts of the plant, aiming the meter at the light source. – Readings need to be taken several times a day, and under cloudy and sunny conditions to determine average light. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

EFFECT OF LIGHT ON GROWTH/DEVELOPMENT Finding Total Solar Radiation Entering Windows • In some cases light requirement of a species will be listed in foot-candles, an old measurement. – Illumination of a surface 1 ft from a standard candle. • Comfortable light for reading is 50 foot-candles, and bright summer daylight is about 10, 000 foot-candles. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

EFFECT OF LIGHT ON GROWTH/DEVELOPMENT Finding Total Solar Radiation Entering Windows • The USDA classified over 100 houseplants by their light requirements: – 75 to 200 foot-candles (767 - 2, 153 luxes) is deemed low. – 200 to 500 foot-candles (2, 153 - 5, 382 luxes) is moderate. – 1, 000+ foot-candles (10, 764 luxes) is high. • Compensation-point intensities—below which respiration exceeds photosynthesis—evaluated as: – 25 foot-candles (229 luxes) for low-light plants – 75 to 100 foot-candles (767 - 1, 076 luxes) for mediumlight species. – 1, 000 foot-candles (10, 764 luxes) for high-light types. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

EFFECT OF LIGHT ON GROWTH/DEVELOPMENT Window Direction • Unobstructed south-facing windows receive the longest duration of daily direct sunlight all year in the northern hemisphere. – Windows receive sun midmorning to late afternoon. • East/west-facing windows provide an intermediate amount of light, less than south, more than north. – In western states, west-facing windows may provide more total solar radiation than in eastern states. • North-facing windows provide the least light but are acceptable for growing a number of species. – Dimness results from the lack of direct sun, only light reflected from the ground or nearby buildings. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

EFFECT OF LIGHT ON GROWTH/DEVELOPMENT Factors Decreasing Window Entry of Sunlight • Overhanging or wide eaves can decrease the time or distance direct sunlight enters a room. – They shade the window when the sun is high in the sky, at midday, and several hours before and after. This effect is more pronounced in the summer than in the winter because the sun is higher off the southern horizon. Figure 17 -6 Effect of eaves on the amount of sunlight entering through a window. Note the depth of penetration into the room. (a) with eaves; (b) without eaves. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

EFFECT OF LIGHT ON GROWTH/DEVELOPMENT Factors Decreasing Window Entry of Sunlight • Tall buildings or fences close to windows can also decrease direct sunlight, a problem of shading from the south, east, or west. – Unlike blockage due to eaves, the problem will be more pronounced in winter. • Shrubs or trees planted close to a window can limit light entry, at times reducing it to only reflected light. – Deciduous trees and shrubs will defoliate in fall, and cause little blockage of light during the crucial winter months. – Evergreens exclude light continuously, and removal or pruning of the plants is the only solution. • Limb up or thin trees • Shrubs should be thinned & headed back to minimize blockage. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

EFFECT OF LIGHT ON GROWTH/DEVELOPMENT Factors Decreasing Window Entry of Sunlight • Most homeowners open curtains or shades in the morning and close them after dark. – Valuable early-morning light can be lost this way. • East-facing windows can lose a substantial portion of their direct sunlight when curtains remain closed after sunrise. – When curtains are open, they can decrease the light area around the outside edge of the window. • Hang curtains so they expose the entire window area when open & avoid valances, which block overhead light. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

EFFECT OF LIGHT ON GROWTH/DEVELOPMENT Factors Decreasing Window Entry of Sunlight • Low-Emittance (Low-E) Window-Glazing Materials have been designed to allow for high solar heat gain, moderate, or low heat gain depending on climate. – Coating a glass surface with a low-emittance material blocks a significant amount of heat from entering. • Low-E coatings are transparent to visible light and transmit 59 to 78% of the light striking the window. – Compared to 81% for normal double-pane windows, and 90 to 95% for single-pane, uncoated glass. • Sufficient for most indoor plants, although it might affect high-light-requiring species and seedlings. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

PLACEMENT FOR OPTIMAL NATURAL LIGHT • Plants can be classified as bright-, medium-, or dimlight-requiring & should be positioned within a room to satisfy their requirements. • The minimum light level at which a plant can maintain itself is called the compensation point. – Light received is enough to photosynthesize carbohydrate for respiration, with no surplus carbohydrate for growth. • With less light, the use of carbohydrate for respiration will exceed its rate of manufacture, and the plant will die slowly. • Decorative plants can be bought at the desired size & maintained in good condition with the correct light. – As the plant is growing very slowly if at all, the time devoted to maintenance is minimal tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

PLACEMENT FOR OPTIMAL NATURAL LIGHT Bright Light The designation “bright”- or “high”light-requiring is given to a number of plants including most flowering species, cacti, and succulents. Difficulty in providing them with sufficient sunlight during darker winter months is the main problem. It is nearly impossible to give brightlight-requiring plants too much light. Most adjust readily to full sunshine and will grow vigorously outdoors during warm weather after they have been acclimated. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. See the entire table on textbook page 327. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

PLACEMENT FOR OPTIMAL NATURAL LIGHT Bright Light While light conditions vary greatly depending on locale, as a general rule, bright-light plants should be placed no farther than 3 feet from a southern window or 2 feet from an east or west window. Figure 17 -7 Suggested distances from windows for growing bright-, medium-, and dim-light plants. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

PLACEMENT FOR OPTIMAL NATURAL LIGHT Moderate Light • Most foliage houseplants have moderate- or medium -light requirements. Adequate light is provided if they are placed up to 6 ft from a southern window, 4 ft from east/west windows, or up to 2 ft from a north window. Moderate-light users grow better when close to the glass, especially in winter. As summer approaches, those in south or west windows should be watched for symptoms of excess light & moved back if symptoms should appear. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. See the entire table on textbook page 328. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

PLACEMENT FOR OPTIMAL NATURAL LIGHT Low Light • Only a small percentage of indoor plants will grow satisfactorily in low light. A number of species classified as moderate-light requirers can survive low-light conditions for several months, unharmed. They will live well in moderate light but generally should not be grown in bright light. Some low-light plants can be injured by excess light. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

MAXIMIZING NATURAL LIGHT Rotation • Plant rotation is proven commercially, and is also practical for the home gardener. – Many large foliage plants in lobbies & malls are rented from interior landscaping & plant maintenance specialists. • Every few months the plants in the low-light display area are replaced and taken back to the greenhouse for recuperation. • During rotation in the greenhouse, they accumulate carbohydrate for respiration when the display area. – The home gardener can move some plants closer to windows and others farther away every 2 to 3 weeks. • This works best on fairly hardy indoor plants & moderateor low-light-requiring species; less so on high-light plants. • Plants in bud should not be moved, as the sudden change in environment can cause the buds to drop. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

MAXIMIZING NATURAL LIGHT Reflective Colors • Once light enters a window, contact with plants can be maximized by light-colored walls, carpets, and drapes which bounce, rather than absorb light. – White walls reflect up to 90% of the light & can contribute significantly to the amount of light plants receive. • Increased reflected light makes it possible to grow moderate- and especially low-light-requiring plants farther from windows. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

MAXIMIZING NATURAL LIGHT Skylights • Skylights are a nearly ideal solution to the problem of insufficient light indoors for growing plants. – Once a very expensive custom construction item, they now are available prefabricated in many sizes/materials. Translucent glass or plastic breaks incoming light rays at the point at which they pass through the material Enables it to illuminate a larger area over a longer time than clear glazing. Figure 17 -8 Light penetration patterns in transparent and translucent skylights. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

ARTIFICIAL LIGHTING FOR PLANT GROWTH • The indoor gardener using artificial lighting can grow almost any flowering plant successfully, as well as herbs, vegetables, and transplants for outdoor use. – Light gardening, as it is called, can be a fascinating hobby. • Two basic types are used for artificial lighting of plants in homes—incandescent & fluorescent lights. – LED (light-emitting diode) lights have come on the market in the past few years and are being used in commercial installations such as hydroponics. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

ARTIFICIAL LIGHTING FOR PLANT GROWTH Photosynthetically Active Radiation (PAR) • The last characteristic addressed is the amount of the types of light necessary for plant growth. – An understanding of the makeup of light, and kinds of light necessary for plant growth is necessary for a gardener to purchase lighting equipment wisely. • Sunlight is naturally suited for plant growth—some artificial light is not. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

ARTIFICIAL LIGHTING FOR PLANT GROWTH Photosynthetically Active Radiation (PAR) • Light energy is divided into wavelengths – Show here is the relationship between wavelengths of visible light and other types of radiant energy. Figure 17 -10 The radiant energy spectrum. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

ARTIFICIAL LIGHTING FOR PLANT GROWTH Photosynthetically Active Radiation (PAR) • Of the energy types listed, only three—ultraviolet, visible, and infrared rays (heat)—are contained in solar radiation and are significant to plant growth. Figure 17 -10 The radiant energy spectrum. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

ARTIFICIAL LIGHTING FOR PLANT GROWTH Photosynthetically Active Radiation (PAR) • Ultraviolet light causes tanning, and plants growing outdoors are exposed to it all day. – It is not necessary for plant growth, and UV light does not pass into glass greenhouses. • Infrared waves transmit heat by traveling through air/space & warming whatever objects they contact. – Infrared in sunlight warm plants outdoors during the day. • At night infrared rays will be given off from previously warmed surfaces like the soil. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

ARTIFICIAL LIGHTING FOR PLANT GROWTH Photosynthetically Active Radiation (PAR) • Light in the orange-red and blue-violet portions of the visible light spectrum have the most significant influence on plant growth. Figure 17 -10 The radiant energy spectrum. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

ARTIFICIAL LIGHTING FOR PLANT GROWTH Photosynthetically Active Radiation (PAR) • Visible light wavelengths compose the majority of photosynthetically active radiation—termed PAR ranging from 400 to 700 nanometers. – The Green and yellow wavelengths are commonly Green yellow reflected by plants. • Giving them their characteristic green appearance. – The Orangeblue. Orange red light and red blue violet light are used violet in photosynthesis. – The red light wavelength has proven to be the range red that triggers flowering in photoperiodic plants. • Whereas blue-violet light is responsible for phototropic responses. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

ARTIFICIAL LIGHTING FOR PLANT GROWTH Types of Lighting - Incandescent • Incandescent lights produce light by channeling electricity through a wire, which heats up and glows. – Compared to fluorescent lights, incandescent lights use more electricity to produce the same amount of light, the extra energy being given off as heat. High in orange-red wavelength, but low in blue-violet, giving objects they light a warm appearance. Red-orange is useful for flowering plants and makes an attractive spotlight, lack of blue-violet makes normal incandescent bulbs alone unsatisfactory for plants. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

ARTIFICIAL LIGHTING FOR PLANT GROWTH Types of Lighting - Incandescent • Incandescent lights produce light by channeling electricity through a wire, which heats up and glows. – Compared to fluorescent lights, incandescent lights use more electricity to produce the same amount of light, the extra energy being given off as heat. Plants grown only under incandescent lighting are paler, thinner, and more etiolated than plants grown under the other light sources listed. In addition, they will not branch, and flowering & subsequent senescence are very rapid. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

ARTIFICIAL LIGHTING FOR PLANT GROWTH Types of Lighting - Fluorescent • Household-Type Fluorescent Lights are long tubes used in specially designed light fixtures. – The inside of the tube is coated with phosphorescent material and has an electrode at each end. • By a chemical reaction with mercury, electricity stimulates the phosphorescent coating to give off light. – They give off almost no heat from the tubes, and only a small amount from the control ballast. – Initially more expensive, fluorescent lights are more economical to operate than incandescent lights. • Up to five times as much light from the same wattage. • They have a much longer life than do incandescent bulbs. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

ARTIFICIAL LIGHTING FOR PLANT GROWTH Types of Lighting - Fluorescent • Wavelengths of light emitted by fluorescent tubes vary depending on the blend of phosphorescent materials used to coat the tube. – Of the normal fluorescent tubes, cool white has been used most often for growing foliage plants. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

ARTIFICIAL LIGHTING FOR PLANT GROWTH Types of Lighting - Fluorescent • Characteristics of plants grown under cool white light are richly colored foliage, slow stem elongation, and proliferous branching. – A sturdy, bushy, and, therefore, attractive plant. However, it is poor in orange-red and should be supplemented by an incandescent light for flowering species. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

ARTIFICIAL LIGHTING FOR PLANT GROWTH Types of Lighting - Plant Lights • Plant lights are commonly available in incandescent and fluorescent styles. – Plant lights are sold in fewer numbers than normal fluorescent tubes, so they are more expensive. Designed to provide light in both blue-violet & orange-red wavelengths, in the best combination for plant growth. Most are of the economical, higher intensity fluorescent type. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

ARTIFICIAL LIGHTING FOR PLANT GROWTH Types of Lighting Figure 17 -11 Light emitted from four types of artificial lighting. A nanometer is one millionth of a meter. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

ARTIFICIAL LIGHTING FOR PLANT GROWTH Types of Lighting - LED • LED ( light-emitting diode) plant lights can save money even over fluorescent lights. – LEDs do not have a ballast as do fluorescent lights. • They operate on less than 20 volts at the bulb, compared to the regular 110 for conventional lights. • There is very little heat produced and no reflector. Grow Master lights use 6 to 9 watts of electricity, and last 10 to 12 years operated 24 hours per day Figure 17 -12 LED plant lights. Photo courtesy of Solar. Oasis Inc. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

ARTIFICIAL LIGHTING FOR PLANT GROWTH Types of Lighting - LED • LED plant lights produce light targeted to the parts of the spectrum that plants use. – Provides additional energy savings over conventional grow lights since no electricity is used for light that is of no benefit to the plant. • LED plant lights deliver light photosynthetically valuable to plants, but relatively dim when perceived by the eye. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

ARTIFICIAL LIGHTING FOR PLANT GROWTH Setting Up a Fluorescent Light Garden • More than one tube is generally needed to grow bright-light-requiring plants such as flowering species and annual or vegetable transplants. – A minimum of two (preferably four) tubes, side by side. • Tubes of 40 watts or more are best, not over 3” apart. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

ARTIFICIAL LIGHTING FOR PLANT GROWTH Setting Up a Fluorescent Light Garden • A homemade light garden is not difficult to construct. – A widely used setup is a shop light containing two tubes and a built-in reflector. • The fixture is mounted on a metal stand or shelving unit, and a lamp timer regulates the hours of operation. Detailed diagrams for homemade light gardens are plentiful in light-gardening and home-building project books and websites. Figure 17 -13 A simple fluorescent light setup for flowering plants. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

ARTIFICIAL LIGHTING FOR PLANT GROWTH Growing Plants under Lights • Success of a light garden is largely determined by… – Distance from the tubes at which plants are grown and number of hours per day lights are on. Because fluorescent lights do not give off heat, there is no problem of heat damage to plants placed too close to the bulbs Figure 17 -14 A full spectrum fluorescent plant light for tabletop use. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

ARTIFICIAL LIGHTING FOR PLANT GROWTH Growing Plants under Lights • In general, 12 to 16 hours per day is considered suitable if there is no additional source of light. – Although foliage plants can grow with less, there is no advantage to running the lights a shorter time except for controlling the photoperiod. • Although fluorescent light bulbs may appear to burn out spontaneously, they actually lose intensity slowly over their entire lifetime of 12, 000 or more hours. – Replace bulbs after about 75% of stated hour-life, as the intensity will have decreased by 15 to 20 percent. • Replacing one bulb every 3 or 4 months will avoid excesslight symptoms from the sudden intensity increase. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

LIGHT-RELATED INDOOR PLANT DISORDERS Insufficient Light • Etiolation of new growth, yellowing and dropping of the older leaves also usually occur. – Plants in the advanced stages of light deficiency have thin weak stems and few leaves. • Such plants should be placed under increased light to recuperate. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

LIGHT-RELATED INDOOR PLANT DISORDERS Excess Light • A plant occasionally will develop symptoms of chronic excess light exposure—such as a lowlight plant grown in a south-facing window. – New leaves will be small and a pale yellowish-green. • Short internodes give a compact, unhealthy appearance. • A more common case is acute excess light damage that occurs when houseplants are placed outdoors after growing indoors all winter. – Sudden increase in intensity destroys the top layers of cells on the leaf surfaces & leaves acquire a silvery cast. • The silvery cast turns brown or bleached yellow in a few days. – Sunburned leaves do not heal—the only way to improve the plant’s appearance is removing them. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

LIGHT-RELATED INDOOR PLANT DISORDERS Excess Light • Bright-light plants will benefit from summer sunlight, but medium-and dim-light species should be placed in shaded or filtered sun areas. – To acclimate houseplants to outdoor conditions, place them in a sheltered outdoor location that receives early morning or late afternoon sun. • After another week bright-light plants can be moved to a brighter outdoor area but still should receive protection. • When bringing the plants indoors again, the acclimatization procedure should be reversed. – Gradually adjusting the plants to decreased indoor light will prevent leaf drop and other signs of light deficiency. tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458

END OF CHAPTER tab Practical Horticulture 7 th edition By Laura Williams Rice and Robert P. Rice, Jr. © 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458